From e46ec89de67d3d8fc91720ae3cba6f9c7a3320b0 Mon Sep 17 00:00:00 2001
From: Krasi Georgiev <krasi-georgiev@users.noreply.github.com>
Date: Mon, 1 Apr 2019 16:23:45 +0300
Subject: [PATCH] use fsync to force persisting the meta file. (#573)

* use fsync to force persisting the meta file.

Signed-off-by: Krasi Georgiev <kgeorgie@redhat.com>
---
 CHANGELOG.md | 1 +
 block.go     | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 51858f3cb7..80f5023041 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
  - [REMOVED] `chunks.NewReader` is removed as it wasn't used anywhere.
  - [REMOVED] `FromData` is considered unused so was removed.
  - [FEATURE] Added option WALSegmentSize -1 to disable the WAL.
+ - [BUGFIX] Fsync the meta file to persist it on disk to avoid data loss in case of a host crash.
 
 ## 0.6.1
   - [BUGFIX] Update `last` after appending a non-overlapping chunk in `chunks.MergeOverlappingChunks`. [#539](https://github.com/prometheus/tsdb/pull/539)
diff --git a/block.go b/block.go
index 2d9c81df91..e08503b641 100644
--- a/block.go
+++ b/block.go
@@ -251,6 +251,11 @@ func writeMetaFile(dir string, meta *BlockMeta) error {
 		merr.Add(f.Close())
 		return merr.Err()
 	}
+	// Force the kernel to persist the file on disk to avoid data loss if the host crashes.
+	if merr.Add(f.Sync()); merr.Err() != nil {
+		merr.Add(f.Close())
+		return merr.Err()
+	}
 	if err := f.Close(); err != nil {
 		return err
 	}